Heat-responsive element



Sept 4, 1945. G. D. BOWER 2,384,153

HEAT-RESPONSIVE ELEMENT Filed April 26, 1941 K I 25 u 20 /A//A/roeGib/P65 0. .80 wig,

M a gag Patented Se t. 14, 1945 UNITED STATES PATENT OFFICEHEAT-BESPONSIVE ELEMENT George D. Bower, University City, Mo., assignorto Automatic Control Corporation, St. Louis, Mo., a corporation ofDelaware Application April as, 1941, Serial No. 390,504 {claim(Ci.'200187) like mechanism'when a reversal of heat conditions occurs ata rate above a critical one. A further obiectis to provide a unit ofthis kind that will not operate the switch when the heat changes occurat rates lower than the critical A further oble'ctof the invention is toprovide a mechanism that will operate from any tem- 'perature ofstarting, and which will not operate upon casual temperature changes,either modulating or ambient.

A further obiectof the invention isto provide a mechanism that willfail'safe, and more particularly one that will shift tosafe positionupon collapse of the flame-receiving parts.

Another object is to provide a unit. that, is adapted for use with asnap action switch while responsive to such heat changes above thepredetermined rate. 1

nthe drawing; A I m of'a furnace or like heat change producing device soas to be influenced upon the production of a heat change at the burner.

The stack unit includes a base portion I! having an extension ll thereonof lesser diameter.

The extension has diametrlcal slots ii at its outer end for a purpose tobe described. The member II has a hole through the axis thereof toreceive an actuating member II. This actuating member has a pin llextending transversely therethrough and engaging within the slots II toprevent rotation between the member II and the actuating member II, butto permit axial displace- I ment.

. Fig. 2 is a horizontal middle section through the mecha w taken on theline 2-2 of Fig. i:

Fig. 3 is a J r vertical section taken on the line 0-8 of Fig, i;

'18:- 41s a vertical section through the tip of the stack unit takenonthe line 4-4 of Fig. 2; is a vertical section through a middle 7 isFig The mechanism includesgenerally a stack unit ll and a unit llmounted on a housin crother, suitable support 12. The unit" II is thestack unit takeninthe line I----! vertical section taken on the line Anopen-ended guard member 2| is secured about the larger part of thesupporting member II and has a plurality of openings ii to permit freeflow of gases through it adjacent its outer portion A first and outerheat-responsive tube 22 is secured at one end to the outer end of thesupporting member ll. At its outer end the tube 22 is formed with aguide 23 extending from the inner surface thereof.

Within the tube 22 there islocated a second or inner tube II whichpreferably is square in cross section. This tube is secured over an endof the actuating member it so that they move together. At its outer endit is guided by the guide ledge ll. Also, at its outer end it has 'acollar 20 secured to it beyond the ledge 21. This collar has projections21 (Fig. 4) at the corners thereof which engageover the ledge 20 so thatuponmovement oi the end of the outer tube 22 outwardly the inner tubemay be carried with it. This, of course, carries the actuating memher I]and Shifts the switches, as will be ex-' Dlained.

Theswitch is of any suitable type. such as is" I! and it may be attachedby the screws that hold the stack unit to the housing. The actuatingmember ll extends within the'casing I! and is threaded at its end toreceive an adjustment adav cd to be into a stack or 'other part upon aprimary lever It pivoted at ii to the casing 30. This primary lever, inturn, acts upon a secondary lever it pivoted on a pair of knife edge Ypivots llcntothecasing.

m lever has a return spring adiacentone end and a switch contact a at,in

otherend;and,asmaybeseen,ithasaninsulating portion between its ends. Theswitch hastwo terminals 4| and 4| from which extend contacts 42 that areadapted to be bridged by the contact element 3! on the secondary lever30. Details oi this mechanism are disclosed in the previously mentionedcopending application or patent. It also may act with two-way contactsalternately closed, as is also shown therein, in which case it willclose with one set or contacts in one position and the other set in itsother position.

Supported on the casing in a molded insulating block is a magnet 44adapted to attract an armature 48 on the end or the secondary lever 36.The armature 4| has two armature elements 46 and 41 held on oppositesides of the projecting magnet legs. One armature element is attractedwith the switch in one position and the other element is attracted withthe switch in the other position. Astop member 4! may be employed tolimit the movement or the secondary lever away irom the contact.

When the actuating member it moves toward the upper part of Pig. 2 thesleeve ii and the washer a move with it. This releases the primarylever, and the secondary lever pivots'under influence oi the spring ll.The secondary lever is. more or less'resilient, and the eilect o! thearmature 4| and the magnet 44 acts with great leverage relative to thatoi! the primary lever. Hence under the force of the spring 18, thesecondary lever flexes until it has stored enough energy to overcome themagnetic attraction. The secondary lever then withdraws the armsture 46,in a snap action manner, because the magnetic effect lessensexponentially with increasing withdrawal. When .the movement of thesecondary lever subsequently brings the armature 41 within range of themagnet, after a dead center position, this armature moves in rapidlyunder an increasing magnetic force to close the contacts with a snapaction, usually accompanied by some early flexing oi the secondarylever.

Upon reverse movement of the actuating member II, the sleeve Si is moveddownwardly to withdraw from the primary lever 35 so that the spring 32,acting upon the washer I3, shifts the primary lever, and in turn thesecondary lever to open the contacts.

The sleeve Ii is adjusted preferably so that at the start the switchcould assume a neutral position, in which the. armatures are balanced onopposite sides or the magnet, and with the tubes moducing no force ofdisplacement either way.

The stack unit It is adapted to be projected into the stack or theheating zone at a suitable distance such as to approximate the sectionline 6-4 onl'ig.2. 'I'hismaybe called the depthoi 2,ss4,1sa

will,however,actuallyremaininapreviously heat from only two sources.Home is derived at its outer end from the flame, but this is of littleeflect. Most of its heat is derived from the outer tube, by radiation,convection, and conduction throughtheendmsatll'. 'Iheresistanoeoi'thesepaths to heatiiow is so great that the inner tube receives less heatthan the outer, and expands muchless,inagiventlrnagaroducingachirnged orplus length diflerential.

Theinnertubeisconstantlydischargingits heat through its end and into themember il,

charged into the cold reservoir is a substantial part of the heatreceived by the inner tube. As a result, the inner tube has a lower heatcontent at its inner end than at its outer, whereas the outer tube,throughout its immersed length, is subjected to infinite heat.

The discharge of heat from the inner tube into the cold reservoir meansthat even though the outer'end of the inner tube becomes as heated asthe outer tube, the inner end of the inner tube will be cooler, and theinnertube will always permit the outer tube to maintain the plus lengthdiiierential.

Even if the inner tube shouldbecome as hot as the outer, so that itattains the starting length 'diflerential, thiswill not mm the switch.because at the starting length differential, the switch u not urgedbeyond dead center of the magnetic snap action, and as noted the switchwill remain in its previously assumed position.

After the heat applied has caused the switch toshiit,andthisnormallyoccursintromoneto three seconds alter flame occurs,a rurther increase in heat of the flame will have no additional eflect,because the most it could do would be to increase the plus lengthdiiierential.

Normal burner fluctuations occurring during operation oi the burner donot cause the device immersion. 'Ihepartsbelowthislinewill'therefore besomewhat cooler than the parts above the -line when heat is applied tothe unit.

oithemembersortheswitchthesecondarylevertoshiittheswitehbecausetheyoocuratratelbelowthecriticslrateoi'fliedeviee. Amonsthei'actorsdeterminingthecrlucslratearethew.plcltyofthemfldwpithlintothe'innerm reiativetothoseotthsoutenandthecorrespondm capscitiesoitheheatnowpathsoutolthe innertube.'lhereisalsoaiasintheswitch meehingintoandretainsdintheinnerhibedurinssame time, the plus length diihrentlal will maintained.

However, when the quanti ytheoutertubeduringagiventimabecomeslethan-thatflowingintoandretainedinthesupplied to the outer tube. This tube can then dissipate its heat notonly to the inner tube as before, but to a greater or lesser degree tothe air in the furnace. more rapidly than can the inner tube, the fiowpaths of which are restricted. When the outer tube loses heat morerapidly than the inner, it contracts more rapidly and produces a minuslength differential, returning the switch to starting position. Thisshifting of the switch can occur from any temperature.

Thereafter, the tubes cool down gradually, with the inner againapproaching the outer, until the starting length difierential isobtained. At this point the switch will remain in its starting position,owing to the previously mentioned balanced setting of the snap actionmeans.

Ordinary fluctuations of ambient temperature when the burner is offoccur at rates too slow to produce a reversal of the length differentialto shift the switch.

What I claim is:

1. In a mechanism of the kind described, a heat-responsive unit havingtwo relatively movable members expansible and contractible in responseto heat changes, and adapted to have a In any case, it can lose heat inga starting length difierential, the application of heat to the unit atrates greater than the heatfiow capacity of the secondmember providing aplus lengthdifierential, and the discharge of heat from the first memberat rates greater than the heat-fiow capacity 01' the second memberproviding a minus length diflerential, a switch having a blade movableto two positions by the production of said plus and minus lengthdiil'erentials, snapactionmeans urging the blade into each of said twopositions, and said heat-responsive unit being adaptedi at said startinglength differential, to

produce "insufilcient blade displacement to move the switch from theposition previously assumed.

3. In a mechanism of the kind described, a base member adapted to besecured to a support, an outer tube projecting from the base member, aninner tube within the outer tube, means attaching the remote ends or thetubes together so that upon expansion of the outer tube the inner may bedisplaced, an actuating rod attached to the rear end of the inner tubeand slidably passing through the base member, switch means on thesupport opposite the base member, said switch means including a primarylever astride the actuating member, a sleeve adjustably threaded intothe actuating member on one side of the primary lever against thesleeve, a secondary lever adapted to be displaced by the primary lever,contact means associated with the secondary lever, a magnet adjacent oneend of the secondary lever, and

starting length differential, the heat-flow capacity of the first memberbeing greater than that of the second, whereby upon application of heatto the unit' at rates greater than the heat-flow capacity of the secondmember the first will ex- Dand more rapidly to provide a plus lengthdifierential, and upon the discharge of heat from the unit at ratesgreater than the heat-flow capacity of the second member, the firstmember will contract more rapidly to provide a minus length differentialupon cessation of heat, an actuated means adapted to be displaced to afirst position upon production of the plus length differential, andadapted to be displaced to a second position upon production of theminus length difierential and means causing said actuated means toremain in either position to which it has been displaced upon subsequentproduction of the starting length difi'erential.

j 2. In a mechanism of the kind described, a

,being shielded to receive heat at a slower rate than the first,heat-absorbing means connected to the second element to absorb 'heattransmitted thereto, said connection being disposed to insure flow ofheat through the second element, said heat-absorbing means beingadapted. normally to continuously absorb heat from the second elementwhenever it attains a temperature above its starting temperature, saidshielding and heat-absorbing means being adapted to provide slower ratesof expansion of the second element than the first upon applicationotheat to the first, and slower rates of contraction of the second uponsharp reduction of heat applied to the first, and said heatabsorbingmeans being adapted normally to .pre-

vent the second element from attaining the starting length diflerentialduring application of heat to the first element, means connecting theelements for displacement of one of them upon increase in length of thefirst one at a rate greater than that or the second, and reversedisplacement of the one upon decrease in length 01' the first one at'arate greater than that of the second, and means adapted to be operatedupon such displacements. i

I GEORGE D. BOWER.

